1. Field of the Invention
This invention is related to systems and methods for continuously circulating fluid through two tubulars as they are being connected or disconnected; and, in certain particular aspects, to continuously circulating drilling fluid through two drill pipes as they are being connected or disconnected. This invention is further related to an improved tong for connecting or disconnecting tubulars in wellbore operations.
2. Description of the Related Art
In many drilling operations in drilling in the earth to recover hydrocarbons, a drill string of a plurality of threadedly-interconnected pieces of drill pipe with a drill bit at the bottom is rotated to move the drill bit. Typically drilling fluid and/or xe2x80x9cmudxe2x80x9d is circulated to and through the drill bit to lubricate and cool the bit and to facilitate the removal of cuttings, debris, etc. from the wellbore that is being formed.
As the drill bit penetrates into the earth and the wellbore is lengthened, more joints of tubular drill pipe are added to the drill string. This involves stopping the drilling while the tubulars are added. The process is reversed when the drill string is removed, e.g. to replace the drilling bit or to perform other wellbore operations. Interruption of drilling may mean that the circulation of the mud stops and has to be re-started when drilling resumes. This can be time consuming, can cause deleterious effects on the walls of the well being drilled, and can lead to formation damage and problems in maintaining an open wellbore. Also, a particular mud weight may be chosen to provide a static head relating to the ambient pressure at the top of a drill string when it is open while tubulars are being added or removed. The weighting of the mud can be very expensive.
To convey drilled cuttings away from a drill bit and up and out of a wellbore being drilled, the cuttings are maintained in suspension in the drilling fluid. If the flow of fluid with cuttings suspended in it ceases, the cuttings tend to fall within the fluid. This is inhibited by using relatively thick drilling fluid; but thicker fluids require more power to pump. Further, restarting fluid circulation following a cessation of circulation may result in the overpressuring of a formation in which the wellbore is being formed.
PCT Application PCT/GB97/02815, (John Lawrence Ayling, applicant) discloses a continuous circulation drilling method in which tubulars are added or removed from a drill string while a drill bit is rotated. In one aspect of this system, a connector is used with an inlet and an outlet for the mud, etc. The system incorporates rams to seal off and separate the flow of mud as a tubular is added or removed.
U.S. Pat. No. 3,559,739 to Hutchinson discloses a method and apparatus for maintaining continuous circulation of foam in a well through a segmented tubing string while the tubing string is being made up or broken up. A chamber having a foam entry port is formed around the tubing string above the wellhead. A valve is provided above the foam entry port to close off the upper portion of the chamber when the tubing string is broken and the upper portion thereof raised above such valve. When it is desired to add or remove a tubing section from the tubing string, the tubing string is held by slips with its open end in the lower portion of the chamber. The upper tubing section is lifted in the chamber to above the valve. The valve is closed and foam is circulated in the chamber through the foam entry port to provide for continuous foam circulation while another section of tubing is added or removed from the tubing string.
There has long been a need for an efficient and effective continuous circulation system for tubular connection and disconnections operations. There has long been a need for such a system which can operate with relatively lower viscosity drilling fluids. There has long been a need for such systems that may be used with either a top drive rig or a rotary table/kelly/kelly-bushing rig.
The present invention, in at least certain preferred embodiments, discloses a continuous circulation system for continuously circulating fluid to a tubular string while a section of tubular is being added or removed. In particular aspects, the tubular string is coiled tubing or a string of drill pipe with a drill bit at its bottom used to drill a wellbore in the earth. Circulation is maintained on such a string during joint makeup and breakout. The present invention further discloses a novel tong that isolates tubulars being handled from high pressure axial loading, thereby preventing the xe2x80x9claunchxe2x80x9d of a tubular from the system, and, which can be used with a standard top drive rig or with a standard kelly and rotary rig.
In one embodiment positioned between a top chamber and a bottom chamber is a gate apparatus that selectively isolates the two chambers and through which may pass the ends of two tubulars that are joined together, that are to be separated, or that are to be joined together. With suitable valving, pumps, control apparatus and devices, and flow lines, fluid flow is maintained to the tubular string beneath the system through the chambers of the system during both xe2x80x9cbreakoutxe2x80x9d and xe2x80x9cmake upxe2x80x9d operations while undesirable leakage of fluid from the system is inhibited or prevented. Seals around each tubularxe2x80x94an upper tubular being added (or removed) from the string and a top tubular of the string situated beneath the upper tubularxe2x80x94prevent fluid from flowing out of the chambers to the environment.
In certain particular aspects the seals in the top chamber and bottom chamber are the stripper rubbers of control heads (rotating or non-rotating). In particular aspects there is an inner bushing or xe2x80x9csabotxe2x80x9d that facilitates a tubular""s entry into and removal from the chamber. This inner bushing or xe2x80x9csabotxe2x80x9d is movably mounted in the system so that it is selectively movable with respect to the stripper rubber to facilitate entry of a tubular end into and through the stripper rubber.
In various particular embodiments the gate apparatus uses one of a variety of structures for sealingly and selectively isolating the top chamber from the bottom chamber; and for providing a selectively operable area through which tubulars may pass during continuous fluid circulation. These gate apparatuses include, in at least certain preferred embodiments, apparatus with a flapper valve, ball valve, plug valve, gate valve or with a blowout preventer (e.g. annular ram-type blind or xe2x80x9cCSOxe2x80x9d type).
The systems and tong of the present invention are particularly suited for underbalanced drilling operations and for extended reach drilling operations. In certain embodiments of systems and methods according to the present invention, faster connection time is achieved. In certain particular aspects in underbalanced drilling with single-phase or two-phase fluids in the wellbore, the need for check valves (or xe2x80x9cstring floatsxe2x80x9d) in a drill string is reduced or eliminated; gas pockets do not need to be rented; and continuous fluid circulation can be maintained. There is no need to wait while circulation is shut off to let gas pressure in the wellbore balance with the atmosphere before a connection can be broken.
By controlling the fluid flow rate within chambers of systems according to the present invention, the threads of tubulars within the chambers are not damaged by the fluid under pressure. In certain systems according to the present invention, the chambers are movable both with respect to a system frame and with respect to a rig floor on which the system is mounted. In certain aspects this allows for heave condensation on offshore rigs. In certain aspects an axial alignment apparatus aligns an upper tubular held by the system.
What follows are some of, but not all, the objects of this invention. In addition to the specific objects stated below for at least certain preferred embodiments of the invention, other objects and purposes will be readily apparent to one of skill in this art who has the benefit of this invention""s teachings and disclosures. It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, nonobvious systems and methods for continuously circulating fluid through a tubular string when a tubular is being connected to or disconnected from the top of the string;
Such systems and methods useful in wellbore drilling operations, including, but not limited to, underbalanced drilling operations and extended reach drilling operations;
Such systems and methods useful with top drive rigs and rotary/kelly rigs;
Such systems and methods with inner bushings or xe2x80x9csabotsxe2x80x9d for facilitating tubulars"" movement with respect to tubular seals or stripper rubbers;
Such systems and methods in which a variety of interchangeable gate apparatuses may be used to provide a sealed central chamber for tubular connection and disconnection;
Such systems and methods that permit operations to be conducted with relatively low viscosity drilling fluid or mud;
Such system and methods that produce wellbores with relatively greater stability due to no or lower pressure shocks to the bore by using relatively low viscosity drilling fluid, by keeping drilling fluid pressure constant and in certain aspects below formation pressure, and without the need to xe2x80x9cbreakxe2x80x9d circulation;
Such systems and methods whose use reduces the risk of stuck pipe by continuously maintaining drilled cuttings in circulation;
Such systems and methods that permit constant or almost constant drilling fluid and mud flow from the wellbore being formed to the equipment that processes the fluids;
Such systems that are closed in which the top of the drill pipe string is not open to the atmosphere; and
Such systems and methods that permit faster connection time in underbalanced drilling operations with two-phase fluids.
Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures and functions. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention.